In one embodiment, the present invention relates to catalysts which are useful in hydrogenation reactions and which comprise the oxides of copper, zinc and aluminum. The preparation of various copper-containing catalysts and the use of such catalysts in various reactions has been described previously. Such reactions include hydrogenation reactions, the synthesis of methanol and higher alcohols from synthesis gas, etc. The copper-containing catalysts also may contain other metal oxides including chromium oxide, zinc oxide, titanium oxide, zirconium oxide, iron oxide, alumina, silica, etc., and mixtures of one or more of said oxides.
The hydrogenation of carboxylic acids and carboxylic esters to alcohols is known in the art, and various methods and catalysts have been suggested for effecting the hydrogenation reaction. For example, the ester may be reduced with lithium aluminum hydride or sodium and alcohol. A commonly practiced method involves the use of a copper-chromite-based hydrogenation catalyst. While copper chromite catalysts are commerically available and successful, the disposal of the spent copper chromite catalyst is a problem since chromium is present in the spent catalyst, and chromium is a highly toxic material which is subject to stringent EPA disposal regulations. Because of the stringent regulations, the cost of the manufacture, use and disposal of copper chromite catalysts has increased. It is anticipated that in the future, more stringent EPA regulations and escalating disposal costs will adversely affect the economics of using a copper-chromite-based catalyst.
U.S. Pat. No. 2,091,800 describes a copper chromite/barium catalyst which is used in a process for hydrogenating esters at a temperature in the range of 200.degree. C. to 400.degree. C. by passing the acid and its esters over the hydrogenation catalyst. Other patents describing various types of copper chromite catalysts used in acid and ester hydrogenation processes include U.S. Pat. Nos. 2,121,367; 2,782,243; 3,173,959; and 3,267,157.
U.S. Pat. No. 3,894,054 describes the production of tetrahydrofuran by catalytic hydrogenation and dehydration of maleic anhydride using a catalyst composition which comprises a mixture obtained by calcining a silica-alumina catalyst and a copper-chromium-zinc catalyst. U.S. Pat. No. 3,971,735 describes the preparation of methanol from syngas with a catalyst comprised of copper, zinc, aluminum and boron. The hydrogenation of esters to alcohols by contacting the ester with hydrogen and a catalyst comprising cobalt, zinc and copper under catalytic hydrogenation conditions is described in U.S. Pat. No. 4,113,662. U.S. Pat. No. 4,279,781 describes a methanol synthesis catalyst which comprises the oxides of copper and zinc and a minor amount of a thermal stabilizing metal oxide such as alumina. The copper to zinc metal-weight ratio is in the range of from 2:1 to 3.5:1. Catalysts comprising copper, cobalt, a metal selected from chromium, iron, vanadium or manganese, a rare earth metal and a small amount of an alkali or alkaline earth metal are described in U.S. Pat. No. 4,291,126. Optionally, the catalyst may contain zinc and/or a noble metal and/or a binder selected from alumina, magnesia and cements. U.S. Pat. No. 4,440,668 describes a three-component oxide catalyst based on copper, a metal from Group VIA, VIIA or VIIIA, and a metal of Group IVA or VA. The preferred catalyst is based on copper, cobalt and zirconium with the first two components being formed by co-precipitation in the presence of the oxide of the third component. Another multi-component catalytic system is described in U.S. Pat. No. 4,513,100 which comprises zinc, chromium, copper, one or more alkaline metals and possibly one or more metals chosen from molybdenum, manganese, lanthanum, cerium, aluminum, titanium and vanadium.
U.S. Pat. No. 4,535,071 describes a catalyst for methanol synthesis from syngas which comprises as catalytically active substances, copper oxide and zinc oxide and as a thermal stabilizing substance, aluminum oxide. Optimum yields of methanol are obtained when the atomic ratio of copper to zinc is between 2.8 and 3.8. Five- component catalyst compositions are described in U.S. Pat. No. 4,551,444 and the essential components are copper, an iron group component, a component of elements 23-26, an alkaline metal compound and a precious metal compound. Catalysts comprising copper oxide and zinc oxide in a ratio of 8:1 to 1:1 are described in U.S. Pat. No. 4,588,848 as being useful in synthesizing neoalcohols from neoacids. U.S. Pat. No. 4,598,061 describes a catalyst for synthesis of methanol and alcohol mixtures from synthesis gas using a catalyst which contains, as an oxide precursor, copper oxide and zinc oxide; aluminum oxide as a thermal stabilizing substance; and at least one alkali metal compound. Catalysts comprising copper and cobalt, and optionally aluminum and/or zinc and/or sodium are utilized in U.S. Pat. No. 4,675,343 for preparing primary aliphatic alcohols from hydrogen and carbon oxides. The catalysts contain a minimum of 3% cobalt. Catalysts containing the oxides of copper, zinc and alumina are described in U.S. Pat. No. 4,704,480 as being useful in the production of aliphatic ketones and an optional consecutive production of the corresponding carbinols. More specifically, catalysts comprising the oxides of copper, zinc and alumina are utilized in Examples 1 and 11 of the patent and a catalyst comprising the oxides of copper and alumina is utilized in Example 12. Copper-zinc catalysts also are described in U.S. Pat. No. 4,808,562, and the catalysts may contain alumina.
U.K. Patent 1,436,773 also describes copper oxide, zinc oxide catalysts obtained by coprecipitation which are suitable for use in the synthesis of methanol from synthesis gas. The ratio of copper to zinc in the catalyst is from 1:1 to 8:1, and the catalyst may contain a thermal stabilizer such as alumina. Japanese Patent 62-53740 apparently describes catalysts derived from the nitrates of copper, zinc, manganese/magnesium and aluminum.
German Offenlegungschrift 2,613,226 describes a continuous preparation of fatty alcohols by catalytic hydrogenation of relatively high molecular weight fatty acids and esters formed with low-molecular weight monohydric alcohols. The process utilizes hydrogen and a catalyst. The catalysts disclosed in the patent include copper chromite or copper-zinc-chromite and copper-zinc catalysts with or without known carrier substances.
Although many copper-containing catalysts have been described in the prior art, there continues to be a need for catalysts which are useful particularly in the hydrogenation of aldehydes, acids and esters, including diesters. It is also desirable to prepare catalysts useful in hydrogenation reactions which can be carried out in either a fixed bed or a fluidized bed reactor.